1. Field of the Invention
This invention relates to the field of musical tuning aids and more specifically to electronic tuning aids having the capability of determining the degree of deviation from theoretically perfect intonation.
2. Prior Art
Tuning of a musical instrument traditionally involved the player listening to a reference note, which may be the note sounded by one of the other players of an ensemble, and adjusting the first player's instrument until the corresponding note is consonant with the reference note. Detection of correct intonation involves a subconscious comparison of the two notes until the combination of the two produces a specified beat note rate, usually, "zero" beat.
The determination of correct intonation is a skill which is acquired as a part of the player's basic musicianship training and which is acquired only after long hours of practice. As with many acquired skills, the accuracy of the intonation which results is a combination of the inherent talent of the performer and the diligence with which the task is pursued.
Attempts have been made to provide additional training aids for the teaching of intonation, by use of electromechanical, mechanical or electronic instruments which can detect the presence or absence of the desired intonation characteristics.
Musicians of lesser skill, such as many members of high school bands and other amateur performing groups are generally greatly assisted by the use of such tuning aids. However, professional players can also benefit from comparison of their intonation with a theoretically perfect standard. A number of tuning aid devices have been proposed to take advantage of these markets, some of which are discussed below.
Prior art frequency meters and tuning aids employ period-measuring circuits which detect the zero-crossings of the output of a suitable transducer. The inverse of period may then be computed and the frequency of the tone thus determined and displayed.
Such instruments can give quite accurate results, but suffer from the drawback that the displayed value has little meaning to a musician who thinks not in terms of physical units but rather in terms of subjective psycho-acoustic phenomena such as "pitch", and who denotes pitch in terms of musical notes, not cycles per second, or Hertz.
A widely used tuning aid, see e.g., Krauss, U.S. Pat. No. 2,806,953, employs rotating discs having the familiar alternating dark and light areas employed for stroboscopic "motion stopping". The strobe light in this case is caused to flash in synchronism with the frequency of the sound impinging upon an input microphone. The patterns on the rotating discs correspond to the various notes of the musical scale. When a particular note is being sounded, the pattern for that note appears to stop. Slightly sharp notes, which are close to the theoretically correct pitch, cause the pattern to appear to move slowly clockwise, while slightly flat notes close to the theoretically correct pitch cause the pattern to appear to move slowly counter-clockwise.
While the stroboscopic disc tuning instrument is effective and accurate and has enjoyed considerable commercial success, it suffers from several drawbacks: (1) it is an electromechanical device and is subject to the usual afflictions which plague such systems; (2) being electromechanical, it is rather expensive; (3) the display is small, and consequently difficult to read at a distance, thereby limiting its usefulness in large rehearsal halls, and; (4) it is easily damaged by shock or mishandling.
The stroboscopic unit has several additional drawbacks which adversely affect its usefulness: (1) it does not produce an audible tone; (2) it is too heavy to be easily carried, and; (3) it is necessary in order to employ the stroboscopic tuner that the user be able to distinguish the direction of rotation of the pattern as well as the rate of rotation, requiring rather close inspection of the rotating discs.
Several variants of the stroboscopic tuning technique have been proposed. For example, Younquist No. 3,901,120 describes a system which detects electronic synchronism between the incoming unknown tone and one of a plurality of reference frequencies. The reference frequencies take the place of the rotating discs while electronic comparators take the place of visual detection of synchronism. Because an electronic comparator provides a useful signal output, any number of displays and any number of different types of displays may be employed. Light-emitting diodes are suggested by Youngquist, thereby eliminating one objection to the stroboscopic technique. However, the difficulty of discerning slightly sharp and flat tuning remains a problem.
Another type of electronic apparatus uses a comparison of a known frequency standard, such as the output frequency of a crystal-controlled oscillator, with the frequency of the unknown signal being measured. Both signals are electronically conditioned to provide a fairly pure sine waveform before they are applied to the vertical and horizontal deflection plates of a cathode ray tube oscillospoce. When the notes are identical in frequency, a circular "Lissajous" pattern is formed on the screen. When sharp or flat, the Lissajous pattern will appear to rotate at a rate which is determined by the magnitude of the departure of the frequency of the unknown signal from the frequency of the reference signal.
A similar oscilliscope-based device employs an oscilloscope having a known horizontal sweep rate which sweep rate is compared with the unknown signal input. When the signal is properly synchronized, a stationary waveform will appear on the oscilloscope screen. When slightly too sharp, the pattern appears to move to the left. When slightly too flat, the pattern appears to move to the right.
The indications available from these oscilloscope-based instruments are ambiguous to the user in that the degree of the inaccuracy of the incoming pitch cannot be readily determined. In the case of the first type of oscilloscope display described, it is difficult to determine both direction (sharp or flat) and the degree of departure from theoretically perfect intonation. Since the user is unable to determine the needed information by merely viewing the oscilloscope screen he can never be absolutely sure of his intonation. Moreoever, as a training aid, these devices are deficient in that they do not readily indicate in which direction the pitch of the unknown signal must be varied in order to bring it closer to the theoretically correct pitch.
A purely electronic approach to determining the frequency of an unknown signal is described by Faber, Jr., et al., U.S. Pat. No. 3,144,802. Faber, et al., employs a conventional digital counter reading a known reference frequency which is gated by the zero crossings of the signal at the unknown signal input. Suitable electronic displays may be devised so that the output is directly readable by the user.
Each of the prior art systems described above suffers from one or more of a group of several disadvantages. First, the display indications are ambiguous in that it is difficult to make an accurate assessment of the degree of departure from perfect intonation. Second, the output indications are also ambiguous in that it is difficult to determine the center frequency of the note being sounded in some cases. Third, the outputs also do not indicate in which direction the information error lies from the theoretically correct intonation. In some of the prior art devices, if the sounded note is not approximately correct, no indication at all can be detected in the tuning aid.
For many of the tuning aids described, unless the player knows, to a fair degree of accuracy, the tone he is attempting to sound, a readout from the tuning aid will not be meaningful. Thus, for example, if a player is attempting to sound a B natural, but is quite sharp, the stroboscopic tuning aid may not register correct pitch either for the B or for the next higher C. In a more extreme case, if the player is extremely sharp, he will be misled by the stroboscopic indicator into believing that he is on correct pitch when he is fingering B natural, but actually sounding a C, unless he makes a careful inspection of the dial indicators for the instruments.
In addition, some of the apparatuses described are heavy and, being electromechanical, are expensive and have a tendency toward unreliability.